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410                         METALLUEGT OF IKON AND STEEL.
steel, but which can be made of the more liquid iron. The attempt has been made to call these "steel/' and the claim has been fortified by analyses showing that the composition resembles that of some steel. On the same basis, the product of the puddle furnace or the charcoal bloomery might be termed mild steel. Malleable iron must always be inferior to steel, because any oxides of silicon, manganese, phosphorus or iron which are formed remain diffused throughout the mass. Such castings are useful in a certain field, for they are far tougher than cast-iron, and they may even enter into competition with steel castings, but they must always bear a different name, since steel castings must be made by pouring into finished shape the melted product of a crucible, a Bessemer converter, or an open-hearth furnace.
SEC. XXb.—Methods of manufacture.—The crucible process is sometimes employed for small castings, since the conditions of the "dead-melt" give a more quiet metal, evolving less gas in contact with cold surfaces, and the casting is more apt to be free from blow-holes. In special cases, as in the manufacture of big guns at Krupp's, the crucible has been used in making large masses of metal, but its great cost prohibits its adoption for general structural work.
Casting plants have been erected with Bessemer converters instead of open-hearth furnaces. These converters are small and the blast is introduced either on the side, just below the surface of the metal, or is directed down on the top of the liquid bath. For each system important benefits are claimed, notwithstanding the fact that Bessemer in his early experiments tried almost every way that could be thought of and abandoned them all for the one in general use today. Side blowing creates a greater amount of heat owing •to the more perfect oxidation of carbon, and to the burning of a proportion of iron. In the ordinary converter much carbonic oxide (CO) escapes, but when the blast is introduced near the surface, and particularly when an auxiliary tuyere delivers air at a little distance above the bath, much of this carbonic oxide is burned to carbonic acid (C02).
In many "small" Bessemer plants the loss of metal is about 20 per cent, and in one case 30 per cent. This greater waste is partly in the cupola and partly in the vessels. The cupolas of a standard Bessemer plant are operated continuously for about three days, and